The present invention pertains to an apparatus which matches the initiation of temperature changeover by a thermostat to a duty cycle of an air temperature conditioning plant.
Current programmable thermostats perform temperature setpoint change, i.e., setback in heating mode, setup in cooling mode, for energy conservation purposes. The current thermostats perform the temperature setpoint change at pre-programmed times without regard to the current "on"/"off" status of the heating/cooling plant at that instant. Further, the temperature setpoint change is without regard to whether the heating/cooling plant can be retained "on" or "off" (without adversely effecting the comfort conditions of the occupants) during the time between the present and the pre-programmed scheduled time for setup/setback. One of the drawbacks of the existing approach is that energy conservation can be reduced if there is a change in the setpoint temperature during the plant "on" cycle due to the setup/setback such that the plant is required to go "off", or if the plant is in an "off" cycle and the inverse occurs. Additionally, such abrupt changes in the plant "on"/"off" status can reduce the plant efficiency and result in equipment short-cycling. At any one instance in time, these drawbacks may sound fairly insignificant; however, over an extended period of time, the amount of energy conserved can be quite significant and the equipment short-cycling can result in a reduction in the expected operating life span of the heating and cooling plant.
With the advent of microprocessor-based electronic thermostats utilizing computers and relevant software as the primary controllers for heating and cooling plants, it has become possible to perform intelligent setup and setback without significant increases in manufacturing costs and without significant software revisions to existing systems by incorporating this invention. Furthermore, energy conservation, which is the primary reason for using programmable thermostats, and an extension in the equipment life can be increased by utilizing this invention.